In silver halide color photographic materials, a dye image is formed by imagewise exposure and development with an aromatic primary amine developing agent to induce a reaction between an oxidation product of the developing agent and a dye image forming coupler (hereinafter simply referred to as "coupler"). In this image forming system, a combination of yellow couplers, cyan couplers and magenta couplers is generally used.
Various pyrazolone derivatives are hitherto known as magenta couplers. The pyrazolone derivatives usually employed in photographic light-sensitive materials are 4-equivalent couplers. For instance, the formation of 1 mol of a dye upon a coupling reaction with an oxidation product of an aromatic primary amine color developing agent theoretically requires development of 4 mols of silver halide. On the other hand, the development of only 2 mols of silver halide is required when using 2-equivalent pyrazolone derivatives having an active methylene group substituted with a group that is releasable upon oxidative coupling with an oxidation product of an aromatic primary amine developing agent. In addition, the 4-equivalent pyrazolone derivatives show a low efficiency in color formation (i.e., conversion of coupler to dye and usually produce only about 1/2 mol of a dye per mol of the coupler.
Hence, it has been heretofore proposed to reduce the amount of silver halide required for development and improve the color formation efficiency by using 2-equivalent pyrazolone magenta couplers. For example, pyrazolone derivatives that release an oxygen atom include 5-pyrazolone having an aryloxy group at the 4-position as described in U.S. Pat. No. 3,419,391 and 5-pyrazolone having an alkoxy group at the 4-position as described in Japanese Patent Publication No. 46453/78.
Examples of pyrazolone derivatives which release a nitrogen atom include compounds having an imidazolyl group, a pyrazolyl group, a triazolyl group, etc. at the 4-position as described in U.S. Pat. Nos. 4,076,533 and 4,241,168; compounds having a pyridonyl group, a 2-oxopiperidinyl group, etc. at the 4-position as described in U.S. Pat. No. 4,220,470; and compounds having a sulfonamido group, etc. at the 4-position as described in U.S. Pat. No. 4,237,217.
Examples of pyrazolone derivatives that release a sulur atom include compounds having a heterocyclic thio group or an arylthio group at the 4-position as described in U.S. Pat. Nos. 3,227,554 and 4,263,723 and Japanese Patent Publication No. 34044/78; compounds having a thiocyano group at the 4-position as described in U.S. Pat. No. 3,214,437; and compounds having a dithiocarbamate group at the 4-position as described in U.S. Pat. No. 4,032,346.
Many of these 2-equivalent couplers can be synthesized from 4-equivalent pyrazolones through a single step. They are also advantageous in terms of sensitivity and equivalency. Inter alia, 5-pyrazolones having a 2-alkoxyarylthio group at the 4-position have specifically proven to be excellent in performance among the sulfur-releasing couplers. The couplers having a 2-alkoxyarylthio group produce a magenta image which is fast to light, while couplers having other arylthio groups produce a magenta image having seriously reduce light fastness.
On the other hand, it is necessary to improve the color reproducibility of the 5-pyrazolone in view of the side absorption observed in the vicinity of 430 nm, a dull cut in the longer wavelength region, and the like. Pyrazoloazole couplers are known magenta couplers which eliminate these disadvantages and are disclosed in Japanese Patent Application (OPI) Nos. 171956/84, 33552/85 and 43659/85.
Color photographic images obtained by using these couplers are usually preserved as photographic records in albums, etc. for a long time or put on exhibition. However, the white background of the image dye is not always resistant to light, heat or humidity and often suffers color change (hereinafter referred to as stain or stain formation) which deteriorates the image qualities when a photographic print or negative, etc. is exposed to light or preserved in high temperature or high humidity conditions over an extended period of time or stored in albums, etc. for many years.
The cause of stain is not clear but many possibilities are considered. For example, the following two assumptions seem probable: (1) Couplers themselves decompose to cause yellowing of the white background; (2) A developing agent remaining in the emulsion layers after the development process is gradually oxidized with oxygen in air, etc. and the resulting oxidation product reacts with couplers (e.g., magenta couplers) to form stain (e.g., magenta stain). Since a magenta color has a high visibility to human eyes, magenta stain particularly brings about a serious reduction in the image quality.
Making the problem more difficult is the fact that it is rare that a new development processing solution is prepared for every development process. In fact, development processing is carried on while the processing solutions are replenished according to the load which is to be processed. The compositions of the processing solutions cannot be simply maintained by making up for the loss due to processing. More specifically, since the development processing solutions generally consist of a color developer, a stopping solution, a bleaching solution, a fixing solution or a blix solution, and the like which are kept at a high temperature of from 31.degree. to 43.degree. C. during processing, the compositions of these processing solutions undergo changes arising from, for example, decomposition or air-oxidation of a developing agent, etc. over a long period of time, accumulation of impurities dissolved out from the photographic materials, carry-over of a processing solution which is adhered to the photographic materials into a next bath, and the like. Restoration of these running solutions is by the replenishment of the shortage of chemicals or by the removal of unnecessary components, but complete restoration cannot be achieved.
When development processing is conducted in such a running solution, components of a developer remain in the photographic light-sensitive materials, thus readily causing stain formation. None of the conventional techniques has succeeded in the effective prevention of stain formation. For instance, it has been proposed to prevent stains by using alkylhydroquinones (e.g., those described in U.S. Pat. Nos. 3,935,016 and 3,960,570, etc.), chromans or coumarans (e.g., those described in U.S. Pat. No. 2,360,290), phenolic compounds (e.g., those described in Japanese Patent Application (OPI) No. 9449/76), sulfinic acid type polymers (e.g., those described in Japanese Patent Application (OPI) No. 151937/81), and the like. Although these compounds are noted to produce more or less of an effect on stains generated during processing, they are virtually ineffective on the prevention of stain formation due to exposure to humidity or heat after color development processing. Japanese Patent Application (OPI) No. 67842/81 discloses that a compound obtained by reacting a nitrogen-containing organic base or a quaternary nitrogen-containing compound with sulfinic acid is incorporated in light-sensitive materials. However, objects of this proposal are essentially different from those of the present invention hereinafter described. That is, one of the objects of the former proposals is to provide a silver halide photographic material which is stable and amendable to rapid processing by incorporating an aromatic primary amine developing agent in the form of a precursor thereof, and another object is to stabilize photographic properties of light-sensitive materials before development processing.